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glucose and fructose, which can be taken up and used by the yeast. S.cerevisiae is glucophilic, which means that although it can use fructose, it consumes the glucose first, sort of like a child who eats the corn on his plate before the peas. The consequence of this is that a wine with residual sugar (fructose) such as late harvest tastes sweeter than if the sweetness were contributed by adding sucrose. Fructose tastes sweeter than sucrose. S. diastaticus is an interesting yeast species descended from S. cerevisiae. Diastase is one of the names for enzymes that break down starch polymers into glucose. The immediate benefit that comes to mind is in distillation to increase yields from the starch of grain feedstocks. This yeast secretes extracellular diastase (more commonly called amylase) to release glucose, which is readily taken up. Starches and dextrins (short residues of starch) can’t be used by yeast. In beermaking, S. diastaticus is considered to be a contaminant because it breaks down dextrins that contribute to desired beer properties and increases the alcohol content. In addition to the various species of Saccharomyces, there are a number of synergies that occur with S. cerevisiae. I used to think that kefir was produced from a species called S. kefir, which contained a beta galactosidase that broke down milk sugar (lactose) into its component sugars, glucose and galactose. In mammalian infants, glucose is always required for energy and galactose is important for brain development. It turns out that S. cerevisiae supports a synergy with lactic acid bacteria such as Lactobacillus and doesn’t have to produce its own beta galactosidase.

A similar situation occurs with sake manufacture. It used to be thought that S. sake was a distinct species of yeast that was highly alcohol tolerant and was used in sake production. It has long been known that the fungus Aspergillus orzae was used to digest rice starch before the alcoholic fermentation and it was thought S. sake was a unique yeast species that could ferment up to 20

British Columbia FRUIT GROWER • Spring 2016 29

per cent alcohol by volume. We now know that selected strains of S. cerevisiae have that property, not a

separate species. S. cerevisiae has become one of the major tools for drug manufacture. It

is a close enough relative to us that it accepts human genes and can express them for the relatively inexpensive manufacture of critical human drugs. Would you like a little insulin in your wine? No problem.

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